Contact material for vacuum switch of wc with co-cu binder and method of making

ABSTRACT

A contact material for a vacuum switch having a composition comprising from 50 to 75 percent of tungsten carbide, from 0.3 to 5 percent of cobalt, and a remainder of copper, said tungsten carbide having a finely pulverized structure of a grain size of less than 1.2 microns.

United States Patent [191 Tazaki et al.

[ CONTACT MATERIAL FOR VACUUM SWITCH OF WC WITH CO-CU BINDER AND METHOD OF MAKING [75] Inventors: Kazuo Tazaki; Hisaji Shinohara;

Akiyoshi Kikuchi; Katsuji Nagami, all of Kawasaki, Japan [73] Assignee: Fuji Denki Seizo Kabushiki Kaisha,

Kamagawa-ken, Japan [22] Filed: Mar. 6, 1973 [21] Appl. No.2 338,568

[30] Foreign Application Priority Data Mar. 7, 1972 Japan 47-023320 [52] US. Cl 29/l82.1, 29/l82.8, 75/200, 75/204 [51] Int. Cl B22f 1/00 [58] Field of Search 29/182.l, 182.8; 75/200, 75/204 [451 Apr. 30, 1974 Primary Examiner-Benjainin R. Padgett Assistant ExaminerB. Hunt Attorney, Agent, or Firm-Holman & Stern ABSTRACT A contact material for a vacuum switch having a composition comprising from 50 to 75 percent of tungsten carbide, from 0.3 to 5 percent of cobalt, and a remainder of copper, said tungsten carbide having a finely pulverized structure of a grain size of less than 1.2 microns.

11 Claims, No Drawings CONTACT MATERIAL FOR VACUUM SWITCH OF WC WITH CO-CU BINDER AND METHOD OF MAKING BACKGROUND OF THE INVENTION This invention generally relates to contact materials and more particularly to a type thereof which is specifically used in vacuum switches operable in a range of from to 20 MVA at 3.3 KV, or from 25 to 50 MVA at 6.6 KV.

It is widely known that W-Cu alloys can be used as contacts in vacuum switches, and that contacts made of these alloys exhibit high resistance against welding of the contacts. It is also found that the contacts made of such materials can minimize the erosion of the contacts due to arcing in the vacuum switch.

Although the tungsten-copper alloys have advantageous features as described above, the material has a drawback in that its so-called chopping level is considerably high.

To overcome this disadvantage, W-Cu alloys containing bismuth have been proposed. However, the W-Cu- Bi alloys were found to be inferior in workability in brazing.

SUMMARY OF THE INVENTION Therefore, a primary object of the present invention is to provide a contact material to be used in a vacuum switch, which is operable with high reliability and has a low chopping level.

Another object of the invention is to provide a contact material for a vacuum switch, which has a minimumrange of variation in the chopping level.

Still another object of the invention is to provide a contact material for a vacuum switch, wherein the value of current above which the contacts tend to be welded is comparable to those in the W-Cu alloys.

These and other objects of the invention can be achieved by a contact material for a vacuum switch, at a composition comprising from 50 to 75 percent of tungsten carbide, from 0.3 to 5 percent of cobalt, and a remainder of copper, said tungsten carbide having a minute pulverized structure of less than 1.2 microns.

DETAILED DESCRIPTION OF THE INVENTION Theinvention will now be described in detail with reference to the following table wherein various tungsten alloys and tungsten carbide alloys are compared ID in the case of a W-Cu alloy. One reason for this is the high melting point of WC. Furthermore, the low chopping level of the WC-Co-Cu alloy according to the present invention can be considered to be also due to the inherent properties of the WC itself.

In view of these considerations, decreasing the content of WC excessively is not desirable, and the addition of excess cobalt is not advantageous because the cobalt reacts with tungsten carbide thereby lowering the melting point of the tungsten carbide.

Upon understanding these effects of WC and Co, various combination thereof may be considered depending on the application requirements. The present invention contemplates the provision of a contact material for a vacuum switch of greater capacities than 10 MVA at 3.3 KV, whereby the composition of the WC-Co-Cu alloy according to the present invention is adapted to be used for such an application.

Practical examples of contacts made of such material illtwwa agi fit A ,WIEXAM LEL, a

Pulverized tungsten carbide of approximately 1.2 microns in grain size was molded under a pressure of 0. l 5

ton/cm, and then presintered in vacuum at 1,400C.

The percentage of voids in the presintered material was 55 percent by volume. The material was thereafter impregnated with 2 percent of Co-Cu alloy in vacuum at 1,300C. The material thus obtained was machined into contacts of approximately 24 mm in diameter, and

As a result, it was found that the chopping level of the contacts was 3.5A, and the interruptable current was more than 4.8 KA. The contacts were not fused toelectricalperformancetests were carried out theregi gether under a current of 20KA flowing therethrougl EXAMPLE 2.

Tungsten carbide powder of 0.7-micron grain size with the material according to the present invention. and cobalt powder of 2-micron gram size were mixed Table Composition Grain size lnterruptable Chopping Gas content by weight) of WC (or W) Current level As will be apparent from the above table, the interruptable current increases when cobalt is added, when the percentage of tungsten carbide becomes low, or

with a ratio of 98:2, and the resulting mixture was press-formed under a pressure of 0.2 ton/cm and presintered in vacuum at 1,300C. The eentie of voids of the presintered material was 42 percent by volume. Thereafter, the presintered material was impregnated with Cu at l,300C in vacuum. The contact material thus obtained was formed into contacts as described in Example I, and electrical performance tests were carried out thereon. As a result, the chopping level was found to be 2.6A, the interruptable current was 4.5 KA, and the current fusing the contacts together was found to be 30 KA.

In the practice of this invention as described above, finely pulverized tungsten carbide is used as the principal component, to which an appropriate amount of Co-Cu alloy is added, and the resulting mixture is formed into desired contacts, whereby interrupters and circuit breakers of high performance and reliability can be produced.

What we claim is:

l. A contact material for a vacuum switch consisting essentially of from about 50 to 75 percent of tungsten carbide having a finely pulverized structure of a grain size of less than 1.2 microns, from 0.3 to 5 percent of cobalt, and a remainder of copper.

2. The contact material as set forth in claim 1 wherein the tungsten carbide is about 60 percent in amount.

3. The contact material as set forth in claim 1 wherein the tungsten carbide is about 70 percent in amount.

4. The contact material as set forth in claim 1 wherein the tungsten carbide is about 75 percent in amount.

5. The contact material as set forth in claim 1 wherein the grain size of the tungsten carbide is 0.7 micron.

6. The contact material as set forth in claim 1 wherein the grain size of the tungsten carbide is 1.2 microns.

7. The contact material as set forth in claim 1 wherein the cobalt is about 2 percent in amount.

8. A method of producing a contact material for a vacuum switch in which a component of tungsten carbide having a finely pulverized structure of a grain size of less than 1.2 microns is press-formed and presintered into a porous structure, which is thereafter impregnated with another components of Co-Cu alloy, the ratio in amount of said components being from about 50 to percent of tungsten carbide, from 0.3 to 5 percent of cobalt, and a remainder of copper.

9. The method as set forth in claim 8 wherein the tungsten carbide is press-formed and presintered in vacuum at approximately 1,400C and is impregnated with the Co-Cu alloy in vacuum at approximately 1,300C.

10. A method of producing a contact material for a vacuum switch in which a component of tungsten carbide having a finely pulverized structure of grain size of less than 1.2 microns is mixed with a component of cobalt to form a mixture thereof, then press-formed and presintered into a porous structure, and is thereafter impregnated with a component of copper, the ratio of said components being from about 50 to 75 percent of tungsten carbide, from 0.3 to 5 percent of cobalt, and a remainder of copper.

11. The method as set forth in claim 10, wherein the tungsten carbide is mixed with the cobalt of approximately 2-micron grain size, then press-formed and presintered in vacuum at approximately l,300C, and is thereafter impregnated with copper in vacuum at approximately 1,300C. 

2. The contact material as set forth in claim 1 wherein the tungsten carbide is about 60 percent in amount.
 3. The contact material as set forth in claIm 1 wherein the tungsten carbide is about 70 percent in amount.
 4. The contact material as set forth in claim 1 wherein the tungsten carbide is about 75 percent in amount.
 5. The contact material as set forth in claim 1 wherein the grain size of the tungsten carbide is 0.7 micron.
 6. The contact material as set forth in claim 1 wherein the grain size of the tungsten carbide is 1.2 microns.
 7. The contact material as set forth in claim 1 wherein the cobalt is about 2 percent in amount.
 8. A method of producing a contact material for a vacuum switch in which a component of tungsten carbide having a finely pulverized structure of a grain size of less than 1.2 microns is press-formed and presintered into a porous structure, which is thereafter impregnated with another components of Co-Cu alloy, the ratio in amount of said components being from about 50 to 75 percent of tungsten carbide, from 0.3 to 5 percent of cobalt, and a remainder of copper.
 9. The method as set forth in claim 8 wherein the tungsten carbide is press-formed and presintered in vacuum at approximately 1,400*C and is impregnated with the Co-Cu alloy in vacuum at approximately 1,300*C.
 10. A method of producing a contact material for a vacuum switch in which a component of tungsten carbide having a finely pulverized structure of grain size of less than 1.2 microns is mixed with a component of cobalt to form a mixture thereof, then press-formed and presintered into a porous structure, and is thereafter impregnated with a component of copper, the ratio of said components being from about 50 to 75 percent of tungsten carbide, from 0.3 to 5 percent of cobalt, and a remainder of copper.
 11. The method as set forth in claim 10, wherein the tungsten carbide is mixed with the cobalt of approximately 2-micron grain size, then press-formed and presintered in vacuum at approximately 1,300*C, and is thereafter impregnated with copper in vacuum at approximately 1,300*C. 